Non-aqueous electrolyte secondary battery

ABSTRACT

A non-aqueous electrolyte secondary battery includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode includes a positive electrode current collector, a positive electrode active material layer on a part of a surface of the positive electrode current collector containing a positive electrode active material, and an insulating layer on other parts of the surface of the positive electrode current collector containing an inorganic filler. The negative electrode includes a negative electrode current collector, and a negative electrode active material layer on a part of a surface of the negative electrode current collector containing a negative electrode active material. The insulating layer includes a first insulating layer disposed along an end portion of the positive electrode active material layer, and a second insulating layer formed at a position separated from the first insulating layer and facing an end portion of the negative electrode active material layer.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.17/068,873, filed Oct. 13, 2020, which claims priority to JapanesePatent Application No. 2019-213200 filed on Nov. 26, 2019, thespecification, claims and abstract of which are incorporated herein byreference in their entireties.

BACKGROUND 1. Technical Field

The present disclosure relates to a non-aqueous electrolyte secondarybattery.

2. Description of Related Art

The non-aqueous electrolyte secondary battery has a high energy densitywith a lightweight, and thus is preferably used as a portable powersupply, a high output power supply mounted on a vehicle, or the like. Inthe non-aqueous electrolyte secondary battery, power storage elementshaving a configuration in which a positive electrode and a negativeelectrode are insulated by a separator or the like are stacked andhoused in one battery case. Here, in the non-aqueous electrolytesecondary battery, in order to suppress the deposition of electrolyteions on the negative electrode, an active material layer of the negativeelectrode may be designed to have a dimension in a width direction widerthan that of an active material layer of the positive electrode.

SUMMARY

In such a type of the non-aqueous electrolyte secondary battery, inorder to more reliably suppress a short circuit between the positiveelectrode and the negative electrode, it has been proposed that aninsulating layer is provided to overlap an end portion of a positiveelectrode active material layer from a surface of a current collectorfor an electrode (for example, see Japanese Unexamined PatentApplication Publication No. 2017-143004 (JP 2017-143004 A). JP2017-143004 A discloses that since an insulating layer is provided witha fine crack formed on a surface or an inside due to paste drying at thetime of manufacturing as a groove, a wall thickness of the groovebecomes thin, and the groove becomes softer than the other portions, andaccordingly, even in a case where a physical load was applied to theinsulating layer, falling off of the insulating layer and the endportion of the positive electrode active material layer can besuppressed. However, the insulating layer that is configured to suppressdesorption or short circuit even if a crack exists may need to contain alarge amount of binder to some extent, have a certain amount ofthickness, or contain a specific type of binder.

The present application provides a non-aqueous electrolyte secondarybattery having a new configuration capable of appropriately suppressinga short circuit between electrodes. In the configuration of thenon-aqueous electrolyte secondary battery disclosed in JP 2017-143004 A,when the insulating layer is provided over a portion where a shortcircuit between a positive electrode and a negative electrode isconcerned, there is room for improvement in terms of an increase in costand manufacturing time (for example, drying time). An aspect of thepresent disclosure provides a non-aqueous electrolyte secondary batteryhaving a new configuration.

That is, the aspect of the present disclosure includes a positiveelectrode, a negative electrode facing the positive electrode, and anon-aqueous electrolyte. The positive electrode includes a positiveelectrode current collector, a positive electrode active material layerwhich is provided on a part of a surface of the positive electrodecurrent collector and contains a positive electrode active material, andan insulating layer which is provided on other parts of the surface ofthe positive electrode current collector and contains an inorganicfiller. The negative electrode includes a negative electrode currentcollector, and a negative electrode active material layer which isprovided on a part of a surface of the negative electrode currentcollector and contains a negative electrode active material. Theinsulating layer includes a first insulating layer disposed along an endportion of the positive electrode active material layer, and a secondinsulating layer formed at a position which is separated from the firstinsulating layer and faces an end portion of the negative electrodeactive material layer.

According to the aspect, the insulating layer is separately formed at aposition along the end portion of the positive electrode active materiallayer and the position facing the end portion of the negative electrodeactive material layer. Accordingly, it is possible to suppress a shortcircuit due to decomposition of the positive electrode active materiallayer, and to appropriately dispose the insulating layer at the positionwhere the short circuit between the positive electrode and the negativeelectrode is likely to occur. Also, since the insulating layer is notprovided excessively, it is possible to suppress an increase in batteryresistance or a decrease in volumetric capacity ratio.

In the aspect, an average thickness of the second insulating layer maybe equal to or greater than a thickness of the negative electrodecurrent collector. According to the aspect, the second insulating layercan suppress a short circuit due to a burr of the negative electrodecurrent collector, which may be formed when the negative electrode iscut.

In the aspect, the first insulating layer may be formed to be interposedbetween the positive electrode current collector and the end portion ofthe positive electrode active material layer and to cover the endportion. According to the aspect, it is possible to suppress, inadvance, a short circuit, due to current concentration at the endportion of the positive electrode active material layer anddecomposition of the positive electrode active material.

In the aspect, an end portion of the negative electrode on a side facingthe second insulating layer may be formed by a cut surface. In otherwords, the end portion of the negative electrode on a side facing thesecond insulating layer may be a cut surface. According to the aspect,as described above, it is possible to suppress a short circuit due tonot only a corner of the negative electrode active material layer butalso a burr of the negative electrode current collector. Therefore, whenthe aspect of the present disclosure is applied to a battery in which anend portion of a negative electrode is formed by a cut surface, aneffect thereof can be remarkably exhibited.

The non-aqueous electrolyte secondary battery according to the aspect ofthe present disclosure can achieve a balance between safety at the timeof overcharging and low resistance. Therefore, for example, when thenon-aqueous electrolyte secondary battery is adopted for a high capacitybattery having a stacked structure in which a plurality of powergenerating elements including a positive electrode and a negativeelectrode is stacked, in particular, the effect thereof is remarkablyexhibited. The non-aqueous electrolyte secondary battery can also beapplied to a secondary battery for applications in which the battery isrepeatedly charged and discharged with a high current at a high rate,and easily reaches a high temperature due to charging and discharging ofa battery itself. Furthermore, the non-aqueous electrolyte secondarybattery can be applied to a secondary battery for applications in whichthe battery is used closely by humans and needs to have high safety.Therefore, the non-aqueous electrolyte secondary battery of the aspectof the present disclosure can be used, for example, as a power supply(main power supply) for driving a vehicle, and especially as a powersupply for driving a hybrid vehicle, a plug-in hybrid vehicle, or thelike.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance ofexemplary embodiments of the disclosure will be described below withreference to the accompanying drawings, in which like signs denote likeelements, and wherein:

FIG. 1 is a cutaway perspective view schematically showing aconfiguration of a non-aqueous electrolyte secondary battery accordingto an embodiment;

FIG. 2 is a partial development view illustrating a configuration of awound electrode body;

FIG. 3 is a sectional view of a main part illustrating a disposition ofinsulating layers of the non-aqueous electrolyte secondary batteryaccording to an embodiment;

FIG. 4 is a schematic sectional view illustrating a configuration of afirst insulating layer;

FIG. 5 is a schematic view illustrating a manufacturing step of apositive electrode according to an embodiment; and

FIG. 6 is a schematic view illustrating a relationship between a diecoater, a shim plate, and a positive electrode.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of a non-aqueous electrolyte secondarybattery disclosed herein will be described. Matters requested forcarrying out the present disclosure (for example, a structure of asecondary battery that does not characterize the present specification),other than matters particularly referred to in the present specification(for example, disposition of an insulating layer) can be understood as adesign matter of those skilled in the art based on the related art inthe field. The present disclosure can be carried out based on thecontents disclosed in the present specification and common generaltechnical knowledge in the field. Dimensional relationships (such aslength, width, or thickness) in the drawings shown below may not reflectactual dimensional relationships. In the present specification, thenotation “A to B” indicating a numerical range means “A or more” and “Bor less”, and for example, includes the meaning of “preferably largerthan A” and “preferably smaller than B”.

In the present specification, the “non-aqueous electrolyte secondarybattery” refers to a general battery that uses a non-aqueous electrolyteas a charge carrier and can be repeatedly charged and discharged as thecharge carrier moves between a positive electrode and a negativeelectrode. An electrolyte in the non-aqueous electrolyte secondarybattery may be, for example, a non-aqueous electrolytic solution, a gelelectrolyte, or a solid electrolyte. Such non-aqueous electrolytesecondary battery includes a lithium polymer battery, a lithium ioncapacitor, and the like, in addition to batteries generally called alithium ion battery and a lithium secondary battery. Although notlimited to the following description, the technology disclosed hereinwill be described by taking the case where the non-aqueous electrolytesecondary battery is a lithium ion secondary battery as an example.

Lithium Ion Secondary Battery

FIG. 1 is a cutaway perspective view showing a configuration of alithium ion secondary battery (hereinafter, simply referred to as“secondary battery”) 1 according to an embodiment. FIG. 2 is a partialdevelopment view illustrating a configuration of a wound electrode body20. FIG. 3 is a sectional view of a main part of the wound electrodebody 20. Reference symbols H and Y in FIGS. 1 to 4 refer to a thicknessdirection and a width direction of an electrode. Further, in the widthdirection Y, a direction toward the center in the width direction may bereferred to as Y1, and a direction toward an opposite side (an endportion side in the width direction) may be referred to as Y2. Note thatthe directions are solely directions determined for convenience ofdescription, and do not limit installation form of the lithium ionsecondary battery at all.

A lithium ion secondary battery 1 includes a flat wound electrode body20, a non-aqueous electrolyte (not shown), and a flat rectangularbattery case 10. The battery case 10 is an outer container that housesthe wound electrode body 20 and the non-aqueous electrolyte. As amaterial of the battery case 10, for example, a metal material havinggood heat conductivity with lightweight, such as aluminum is preferred.The battery case 10 includes a bottomed rectangular parallelepiped casebody 11 having an opening, and a lid member (sealing plate) 12 thatcloses the opening. A lid member 12 is a rectangular plate member. Apositive electrode terminal 38 and a negative electrode terminal 48 forexternal connection project from the lid member 12 toward the outside ofthe case.

The wound electrode body 20 is formed in a manner that a strip-shapedpositive electrode 30 and a strip-shaped negative electrode 40 arestacked in a state of being insulated by a strip-shaped separator 50,and wound with a width direction orthogonal to the longitudinaldirection as a winding axis WL. The wound electrode body 20 has a flatshape and has an oval shape in a section in the width direction Y. Thewidth direction of the battery case 10 in FIG. 1 is a directioncoinciding with the winding axis WL of the wound electrode body 20.

The positive electrode 30 includes a positive electrode currentcollector 32, a positive electrode active material layer 34, and aninsulating layer 36. The positive electrode current collector 32 holdsthe positive electrode active material layer 34 and the insulating layer36 on a surface thereof. The positive electrode current collector 32 hasother region (hereinafter referred to as a non-coated portion) that doesnot hold the positive electrode active material layer 34 and theinsulating layer 36. The positive electrode active material layer 34 isa porous body containing a positive electrode active material and can beimpregnated with an electrolytic solution. The positive electrode activematerial releases or stores lithium ions, which are charge carriers, toor from the electrolytic solution. The positive electrode activematerial layer 34 is provided on a part of the surface (one surface orboth surfaces) of the positive electrode current collector 32. Thepositive electrode current collector 32 is a member configured to supplyor collect charges to or from the positive electrode active materiallayer 34. The positive electrode current collector 32 iselectrochemically stable in a positive electrode environment in abattery and is more preferably formed of a conductive member made of ametal having good conductivity (such as aluminum, an aluminum alloy,nickel, titanium, and stainless steel).

In the positive electrode active material layer 34, typically, a powderypositive electrode active material is bonded together with a conductivematerial by a binder (binding agent) and is bonded to the positiveelectrode current collector 32. As the positive electrode activematerial, various materials used in the related art as a positiveelectrode active material of a lithium ion secondary battery can be usedwithout particular limitation. Preferred examples thereof includeparticles of an oxide (lithium transition metal oxide) containinglithium and a transition metal element as constituent metal elements,such as lithium nickel oxide (for example, LiNiO₂), lithium cobalt oxide(for example, LiCoO₂), lithium manganese oxide (for example, LiMn₂O₄),and composites of thereof (for example, LiNi_(0.5)Mn_(1.5)O₄ andLiNi_(1/3)Co_(1/3)Mn_(1/3)O₂), and particles of phosphate containinglithium and a transition metal element as constituent metal elements,such as lithium manganese phosphate (LiMnPO₄) and lithium iron phosphate(LiFePO₄). Such a positive electrode active material layer 34 can beproduced, for example, by supplying a positive electrode paste, obtainedby dispersing a positive electrode active material, a conductivematerial, and a binder (for example, acrylic resin such as a methacrylicacid ester polymer, vinyl halide resin such as polyvinylidene fluoride(PVdF), and polyalkylene oxide such as polyethylene oxide (PEO)) in anappropriate dispersion medium (For example, N-methyl-2-pyrrolidone), tothe surface of the positive electrode current collector 32 and thenremoving the dispersion medium by drying. In the configuration includingthe conductive material, as the conductive material, for example, acarbon material such as carbon black (typically, acetylene black orKetjenblack), activated carbon, graphite, and carbon fiber can bepreferably used. The materials may be used alone or two or more kindsthereof may be used in combination.

As shown in FIG. 4 , the positive electrode active material layer 34has, in a sectional view, a flat region A1 where the surface of thepositive electrode active material layer 34 is flat and has asubstantially uniform thickness, and an end portion region A2 where thesurface of the positive electrode active material layer 34 is curvedtoward the positive electrode current collector 32 toward an end portionE. The flat region A1 is formed on the surface of the positive electrodecurrent collector 32. The flat region A1 is in contact with the surfaceof the positive electrode current collector 32. Although notparticularly limited, an average thickness of the flat region A1 may beapproximately 10 to 200 typically 20 to 150 for example 40 to 100 Theflat region A1 herein includes the center of the positive electrodeactive material layer 34 in the width direction Y. The flat region A1has a width Lm in the width direction Y.

The end portion region A2 extends from the flat region A1 in the Y2direction. The entire end portion region A2 may be formed on the surfaceof the positive electrode current collector 32. In some embodiments, atleast a part of the end portion region A2 may be formed on a surface ofthe first insulating layer 36 a to be described later. A part of the endportion region A2 shown in FIG. 4 is stacked on the first insulatinglayer 36 a. The end portion region A2 herein is formed from the surfaceof the positive electrode current collector 32 to the surface of thefirst insulating layer 36 a. The end portion region A2 has a width Le inthe width direction Y The width Le is shorter than the width Lm of theflat region A1 in usual. Although not particularly limited, the width Lemay be approximately 10 μm or larger, typically 20 to 10000 μm, forexample, 30 to 5000 μm, or to 500 μm. In the sectional view, the endportion region A2 has an inclined surface S1 having a thickness thatcontinuously decreases toward the end portion of the positive electrodecurrent collector 32 in the Y2 direction, and an inclined surface S2having a thickness that continuously decreases toward the end portion ofthe positive electrode current collector 32 in the Y1 direction,contrary to the inclined surface S1. At least a part of the inclinedsurface S1 is typically covered with the first insulating layer 36 a. Inthe configuration having the inclined surface S2, the entire inclinedsurface S2 is covered with the first insulating layer 36 a. The endportion region A2 is not exposed in a plan view.

The insulating layer 36 includes an inorganic filler and a binder andhas an electrical insulation property. Such an insulating layer 36 istypically formed by binding the inorganic filler to each other and tothe positive electrode current collector 32, with the binder. Theinsulating layer 36 may be a porous layer that enables the chargecarriers to pass. The insulating layer 36 includes the first insulatinglayer 36 a and the second insulating layer 36 b, for example, as shownin FIGS. 2 and 3 . The first insulating layer 36 a is disposed along theend portion of the positive electrode active material layer 34. Thefirst insulating layer 36 a is disposed along the end portion of thepositive electrode active material layer 34 on a side where thenon-coated portion 32A is provided (that is, in the Y2 direction). Thesecond insulating layer 36 b is provided at a position separated fromthe first insulating layer 36 a. In other words, the non-coated portion32A is provided between the first insulating layer 36 a and the secondinsulating layer 36 b. The non-coated portion 32A is provided on anotherside of the second insulating layer 36 b different from the positiveelectrode active material layer 34 and the first insulating layer 36 a(that is, the Y2 direction). The second insulating layer 36 b is formedat a position facing the end portion of the negative electrode activematerial layer 44 of the negative electrode 40 that faces the secondinsulating layer 36 b.

As shown in FIG. 4 , the first insulating layer 36 a is formed with apredetermined width Lc in the width direction. The width Lc is adistance between the end portion E of the positive electrode activematerial layer and the end portion of the first insulating layer 36 a inthe Y2 direction. The first insulating layer 36 a is positioned at aboundary between the positive electrode active material layer 34 and thenon-coated portion 32A in the width direction. Microscopically, forexample, the first insulating layer 36 a may be interposed between thepositive electrode current collector 32 and the end portion E of thepositive electrode active material layer 34, as shown in FIG. 4 .Further, the first insulating layer 36 a may be disposed to cover atleast a part of the inclined surface S1 of the positive electrode activematerial layer 34, and may be disposed such that a part thereof coversan upper surface of the positive electrode active material layer 34. Insome examples, for example, as shown in FIG. 4 , the first insulatinglayer 36 a may cover the entire inclined surface S1 of the positiveelectrode active material layer 34. In the end portion region A2, forexample, an overlapping portion B in which the first insulating layer 36a that has been interposed between the positive electrode currentcollector 32 and the inclined surface S2, the end portion region A2 ofthe positive electrode active material layer 34, and the firstinsulating layer 36 a that is stacked on the inclined surface S1 arestacked from the side close to the positive electrode current collector32 may be formed. The overlapping portion B herein has an upper andlower three-layer structure. A width of the overlapping portion B is adimension Lb by which the first insulating layer 36 a is interposedbetween the positive electrode current collector 32 and the positiveelectrode active material layer 34. The maximum thickness of theoverlapping portion B may be equal to or smaller than the averagethickness of the flat region A1.

As shown in FIG. 3 , the second insulating layer 36 b is disposed bybeing separated from the first insulating layer 36 a in the widthdirection Y. The second insulating layer 36 b is positioned toward a Y1direction side and a Y2 direction side from the end portion X(hereinafter, may be referred to a point X) of the negative electrode 40in the Y2 direction. Both sides of the second insulating layer 36 b inthe width direction are sandwiched by the non-coated portion 32A. Thus,in the positive electrode 30, the positive electrode active materiallayer 34, the first insulating layer 36 a, the non-coated portion 32A,the second insulating layer 36 b, and the non-coated portion 32A aredisposed consecutively in this order along the width direction Y.

Here, although not limited to the following width, the width Lc of thefirst insulating layer 36 a may be 20% Ld or greater, when a distancebetween the end portion E of the positive electrode active materiallayer 34 and the end portion X of the negative electrode 40 in the Y2direction is Ld. The width Lc has a relationship with the dimension ofthe second insulating layer 36 b to be described later, and may be 25%Ld or greater, or 30% Ld or greater. However, depending on therelationship with the dimension of the second insulating layer 36 b tobe described later, the width Lc is appropriately approximately 60% Ldor smaller, and may be 50% Ld or smaller, 40% Ld or smaller, 30% Ld orsmaller, or 25% Ld or smaller.

Also, a separation distance between the first insulating layer 36 a andthe second insulating layer 36 b is appropriately 10% Ld or longer, andmay be 20% Ld or longer, 30% Ld or longer, 40% Ld or longer, or 50% Ldor longer. However, it is appropriate that the separation distance is60% Ld or shorter in view of the dimension relationship between thefirst insulating layer 36 a and the second insulating layer 36 b.

A dimension L1 of a portion of the second insulating layer 36 bextending from the end portion X toward the Y1 direction is not limited,and may be 20% Ld or greater. The dimension L1 has a relationship withthe dimension of the first insulating layer 36 a or the separationdistance described above, and may be 25% Ld or greater, or 30% Ld orgreater. Note that considering the dimension of the first insulatinglayer 36 a or the separation distance, the dimension L1 is appropriatelyapproximately 60% Ld or smaller, and may be 50% Ld or smaller, 40% Ld orsmaller, 30% Ld or smaller, or 25% Ld or smaller.

Also, a dimension L2 of a portion of the second insulating layer 36 bextending from the end portion X toward the Y2 direction is not limited,and may be 20% Ld or greater. The dimension L2 is preferably short fromthe viewpoint of reducing the resistance of the lithium ion secondarybattery 1, reducing foil collecting defects, or the like. From theviewpoint described above, the dimension L2 may be 50% Ld or smaller,and is appropriately 40% Ld or smaller or 30% Ld or smaller.

As the inorganic filler that forms the insulating layer 36, it ispossible to use a material that does not soften or melt at a temperatureof 600° C. or higher, typically 700° C. or higher, for example, 900° C.or higher, and has heat resistance and electrochemical stability toextent that the insulation between the positive electrode and thenegative electrode can be maintained. Typically, the inorganic fillercan be formed of the above-described inorganic material having the heatresistance and insulation property, a glass material, a compositematerial thereof, and the like. Specific examples of such inorganicfiller include inorganic oxides such as alumina (Al₂O₃), magnesia (MgO),silica (SiO₂), and titania (TiO₂), nitrides such as aluminum nitride andsilicon nitride, metal hydroxides such as calcium hydroxide, magnesiumhydroxide, and aluminum hydroxide, clay minerals such as mica, talc,boehmite, zeolite, apatite, and kaolin, and glass materials. Among thematerials, as the inorganic filler, it is preferable to use boehmite(Al₂O₃·H₂O), alumina (Al₂O₃), and silica (SiO₂), which have stablequality and are easily available, and boehmite having an appropriatehardness is more preferred. Any one of the materials may be containedalone, or two or more kinds thereof may be included in combination.

As the binder contained in the insulating layer 36, for example, variousbinders that can be used in the positive electrode active material layercan be preferably used. Among the binders, a vinyl halide resin such aspolyfluoride vinylidene (PVdF) can be preferably used as the binder,from the viewpoint that the insulating layer 36 having an appropriatethickness is preferably formed while the binder imparts flexibility tothe insulating layer 36 when a plurality of positive electrode currentcollectors 32 is bundled to collect current. A proportion of the bindercontained in the insulating layer 36 is typically 1% by mass or more,preferably 5% by mass or more, and may be 8% by mass or more or 10% bymass or more. The binder contained in the insulating layer 36 is, forexample, typically 30% by mass or less, 25% by mass or less, 20% by massor less, 18% by mass or less, and 15% by mass or less. As a typicalexample, the proportion may be appropriately adjusted to 5% to 20% bymass. A basis weight of the insulating layer 36 may be approximately 0.5mg/cm² or more, 0.7 mg/cm² or more, or 1 mg/cm² or more, and may be 1.5mg/cm² or less, 1.3 mg/cm² or less, and 1.2 mg/cm² or less.

The insulating layer 36 may be configured to prevent a short circuitbetween the positive electrode current collector 32 and the negativeelectrode active material layer 44 from occurring, for example, evenwhen the lithium ion secondary battery 1 is exposed to a hightemperature environment of 150° C. From the viewpoint as describedabove, the thickness of the insulating layer 36 is preferably 3 μm orlarger, and more preferably 4 μm or larger. Here, the short circuitbetween the positive electrode 30 and the negative electrode 40 is notlimited to the short circuit between the positive electrode currentcollector 32 and the negative electrode active material layer 44. Forexample, in the positive electrode current collector 32, since a softaluminum foil is generally used, and thus, burrs are difficult to begenerated at the time of cutting. On the other hand, a copper foil,which is often used as the negative electrode current collector 42, maygenerate burrs having a relatively high height along the thicknessdirection, at the time of cutting. The burrs of the negative electrodecurrent collector 42 locally concentrate the current during overchargingto form a high potential region, which may deteriorate or decompose theelectrolytic solution, the separator, and the positive electrode activematerial in the vicinity thereof. Therefore, the second insulating layer36 b preferably has a thickness that can eliminate the adverse effect ofthe burrs of the negative electrode current collector 42. The burrs ofthe type of negative electrode current collector 42 are rarely formed tobe higher than the thickness of the negative electrode current collector42 itself. From the viewpoint described above, the thickness of thesecond insulating layer 36 b (which may be the insulating layer 36) ispreferably equal to or greater than the thickness of the negativeelectrode current collector 42. The second insulating layer 36 b (whichmay be the insulating layer 36) having an excessively large thickness isnot preferable from the viewpoint of directly increasing the cost ordecreasing the capacity density per unit weight. From the viewpoint asdescribed above, the thickness of the insulating layer 36 may betypically 20 μm or smaller, for example, 18 μm or smaller, 15 μm orsmaller, or 10 μm or smaller (for example, less than 10 μm), or may be 8μm or smaller.

An average particle diameter of the inorganic filler is not particularlylimited. From the viewpoint of preferably forming the insulating layer36 having the thickness, the average particle diameter is typically 3 μmor smaller, preferably 2 μm or smaller, and for example, 1 μm orsmaller. However, a too fine inorganic filler is inferior inhandleability or uniform dispersibility, and thus not preferable.Therefore, the average particle diameter of the inorganic filler istypically 0.05 μm or larger, preferably 0.1 μm or larger, for example0.2 μm or larger. The average particle diameter is the cumulative 50%particle diameter in volume-based particle size distribution obtained bya laser diffraction scattering method, similar to the positive electrodeactive material and the like.

The negative electrode 40 is configured by providing the negativeelectrode active material layer 44 on the negative electrode currentcollector 42. The negative electrode current collector 42 is providedwith a non-coated portion 42A where the negative electrode currentcollector 42 is exposed, without forming the negative electrode activematerial layer 44 for current collection. The negative electrode activematerial layer 44 contains a negative electrode active material.Typically, the particulate negative electrode active materials may bebonded to each other by a binder (binding agent) and may be bonded tothe negative electrode current collector 42. The negative electrodeactive material stores and releases lithium ions, which are chargecarriers, from or to the electrolytic solution in accordance withcharging and discharging. As the negative electrode active material,various materials used in the related art as a negative electrode activematerial of a lithium ion secondary battery can be used withoutparticular limitation. Preferred examples thereof include carbonmaterials typified by artificial graphite, natural graphite, amorphouscarbon, and composites thereof (for example, amorphous carbon-coatedgraphite), or lithium storage compounds such as a material, such assilicon (Si), forming an alloy with lithium, lithium alloys thereof(such as Li_(X)M, M is C, Si, Sn, Sb, Al, Mg, Ti, Bi, Ge, Pb, or P, andX is a natural number), and a silicon oxide (SiO). The negativeelectrode 40 can be produced, for example, by supplying a negativeelectrode paste obtained by dispersing a powdery negative electrodeactive material and a binder (for example, rubbers such asstyrene-butadiene copolymers (SBR) and acrylic acid-modified SBR resin(SBR latex) and cellulosic polymers such as carboxymethyl cellulose(CMC)) in an appropriate dispersion medium (for example, water orN-methyl-2-pyrrolidone, preferably water), to the surface of thenegative electrode current collector 42, and then removing thedispersion medium by drying. As the negative electrode currentcollector, a conductive member made of a metal having a goodconductivity (for example, copper, nickel, titanium, and stainlesssteel, typically the copper) can be preferably used.

The separator 50 is a component that insulates the positive electrode 30and the negative electrode 40 from each other and provides a movementpath of the charge carriers between the positive electrode activematerial layer 34 and the negative electrode active material layer 44.Such separator 50 is typically disposed between the positive electrodeactive material layer 34 and the negative electrode active materiallayer 44. The separator 50 may have a function of holding thenon-aqueous electrolytic solution and a shutdown function of closing themovement path of the charge carriers at a predetermined temperature.Such separator 50 can be preferably configured by a microporous resinsheet made of resin such as polyethylene (PE), polypropylene (PP),polyester, cellulose, and polyamide. Among the microporous sheet made ofresins, the microporous sheet made of polyolefin resin such as PE and PPhas the shutdown temperature that can be preferably set in a range of80° C. to 140° C. (typically 110° C. to 140° C., for example 120° C. to135° C.), and thus is preferable. The shutdown temperature is atemperature at which the electrochemical reaction of the battery isstopped when the battery generates heat, and shutdown is typicallyexpressed by melting or softening the separator 50 at the temperature.The separator 50 may have a single-layer structure formed of a singlematerial, and may have a structure in which two or more kinds ofmicroporous resin sheets having different materials or properties (forexample, average thickness and porosity) are stacked (for example, athree-layer structure in which PP layers are stacked on both sides of PElayer).

A thickness (average thickness, the same is applied to the followings)of the separator 50 is not particularly limited, and can be usually 10μm or larger, typically 15 μm or larger, and for example, 17 μm orlarger. An upper limit thereof can be 40 μm or smaller, typically 30 μmor smaller, and for example 25 μm or smaller. When the average thicknessof a substrate is within the above range, permeability of the chargecarriers can be favorably maintained, and a minute short circuit(leakage current) is less likely to occur. Therefore, both theinput-output density and safety can be achieved at a high level.

As the non-aqueous electrolytic solution, typically, those obtained bydissolving or dispersing a supporting salt as an electrolyte in anon-aqueous solvent (for example, lithium salt, sodium salt, andmagnesium salt, and the lithium salt in a lithium ion secondary battery)can be used without particular limitation. Alternatively, thenon-aqueous electrolyte may be a so-called polymer electrolyte or solidelectrolyte in which a polymer is added to a liquid non-aqueouselectrolyte to form a gel. As the non-aqueous solvent, it is possible touse various organic solvents such as carbonates, ethers, esters,nitriles, sulfones, and lactones, which are used as the electrolyticsolution in a general lithium ion secondary battery without anyparticular limitation. Specific examples thereof include chaincarbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC),and ethylmethyl carbonate (EMC), and cyclic carbonates such as ethylenecarbonate (EC) and propylene carbonate (PC). Among the examples, it ispreferable to partially include a solvent (for example, a cycliccarbonate) which is decomposed in an acidic atmosphere of the positiveelectrode to generate hydrogen ions. Such non-aqueous solvent may befluorinated. Also, one kind of the non-aqueous solvents may be usedalone or two or more kinds thereof can be used in a mixed solvent. Asthe supporting salt, various salts used in general lithium ion secondarybatteries can be appropriately selected and used. For example, a lithiumsalt such as LiPF₆, LiBF₄, LiClO₄, LiAsF₆, Li(CF₃SO₂)₂N, and LiCF₃SO₃ isused. In the technology disclosed herein, the effect of suppressing heatgeneration during overcharge can be obtained. Therefore, for example,when a lithium compound containing fluorine that is decomposed duringovercharge to generate hydrogen fluoride (HF) is used as the supportingsalt, the effect of the present technology is easily exhibited, and thusis preferable. Such supporting salts may be used alone or two or morekinds thereof may be used in combination. The supporting salt ispreferably prepared such that a concentration in the non-aqueouselectrolyte falls within the range of 0.7 mol/L to 1.3 mol/L.

Further, the non-aqueous electrolyte may contain various additives andthe like as long as the characteristics of the lithium ion secondarybattery of the present disclosure are not impaired. As the additives, agas generating agent, a film forming agent, or the like may be used forone or more purposes such as improving the input-output characteristicsof the battery, improving the cycle characteristics, and improving theinitial charge-discharge efficiency. Specific examples of the additivesinclude an oxalato complex compounds such as fluorophosphate (preferablydifluorophosphate; for example, lithium difluorophosphate represented byLiPO₂F₂) and lithium bis(oxalato)borate (LiBOB). It is suitable that theconcentration of the additives in the whole non-aqueous electrolyte isusually 0.1 mol/L or less (typically 0.005 mol/L to 0.1 mol/L).

The lithium ion secondary battery 1 shown in FIG. 1 uses a flatrectangular battery case as the battery case 10. However, the batterycase 10 may be a non-flat rectangular battery case, a cylindricalbattery case, or a coin battery case. Alternatively, the battery case 10may be a laminated bag formed by laminating a metal battery case sheet(typically an aluminum sheet) and a resin sheet in a bag shape. Further,for example, the battery case may be made of aluminum, iron, alloys ofthe metals, and high-strength plastic. The lithium ion secondary battery1 shown in FIG. 1 includes a so-called wound electrode body 20. As shownin FIG. 2 , a width W1 of the positive electrode active material layer34, a width W2 of the negative electrode active material layer 44, and awidth W3 of the separator satisfy the relationship of W1<W2<W3. Inaddition, the negative electrode active material layer 44 covers thepositive electrode active material layer 34 at both end portions in thewidth direction, and the separator 50 covers the negative electrodeactive material layer 44 at both end portions in the width direction.However, the wound electrode body 20 of the lithium ion secondarybattery 1 disclosed herein is not limited to the wound electrode body,and for example, may be a so-called flat plate type electrode body 20having a form in which a plurality of positive electrodes 30 andnegative electrodes 40 is stacked by being insulated by the separator50. Alternatively, a single cell in which one positive electrode 30 andone negative electrode 40 are housed in the battery case.

The lid member 12 of the battery case 10 may be provided with a safetyvalve configured to discharge gas generated inside the battery case tothe outside or an injection port by which an electrolytic solution isinjected, similar to the battery case of a lithium ion battery of therelated art. Further, the lid member 12 is provided with the positiveelectrode terminal 38 and the negative electrode terminal 48 forexternal connection in a state of being insulated from the battery case10. The positive electrode terminal 38 and the negative electrodeterminal 48 are electrically connected to the positive electrode 30 andthe negative electrode 40 via a positive electrode current collectingterminal 38 a and a negative electrode current collecting terminal 48 a,respectively, and are configured to be able to supply power to anexternal load (see FIG. 1 ).

Method of Manufacturing Positive Electrode

A method of manufacturing the positive electrode 30 as described aboveis not limited. In some embodiments, for example, the positive electrode30 can be produced by a manufacturing method including the followingsteps:

-   -   (S1) preparing positive electrode paste for forming a positive        electrode active material layer;    -   (S2) preparing insulating layer paste for forming an insulating        layer;    -   (S3) coating with the paste and drying the paste; and    -   (S4) slitting.

Steps (S1) and (S2) are in no particular order, and either step may beperformed first or both steps may be performed at the same time.Further, Step (S4) is optional and can be omitted in another embodiment.Hereinafter, the steps will be described in order.

In Steps (S1) and (S2), positive electrode slurry and insulating layerslurry are prepared, respectively. The positive electrode slurry and theinsulating layer slurry can be prepared by dispersing the materialforming the positive electrode active material layer 34 or theinsulating layer 36 in an appropriate dispersion medium (such as wateror NMP) and adjusting the viscosity and the like.

The paste can be prepared using a stirring or mixing device such as aball mill, a roll mill, a planetary mixer, a disperser, or a kneader.

Viscosity V1 of the positive electrode active material layer-formingpaste may be adjusted to a range of approximately 1,000 to 20,000 mPa·s,typically 5,000 to 10,000 mPa·s. The viscosity V1 can be adjusted by,for example, the solid content (for example, a constituent material orthe binder) with respect to the solvent, an addition amount of theviscosity modifier, the kneading time of the paste, and the like. As aresult, Step S3 to be described later can be stably and accuratelyperformed. In the present specification, the “viscosity of paste” refersto a value measured at 25° C. with a rheometer at a shear rate of 21.5s⁻¹.

The viscosity V2 of the insulating layer forming paste may be adjustedto a range of approximately 1000 to 5000 mPa·s, for example 1500 to 4500mPa·s. The viscosity V2 can be adjusted by, for example, the solidcontent (for example, a constituent material or the binder) with respectto the solvent, an addition amount of the viscosity modifier, thekneading time of the paste, and the like. As a result, Step S3 to bedescribed later can be stably and accurately performed.

In step S3 to be described later, when the so-called simultaneouscoating method is adopted, the viscosity V2 of the insulating layerforming paste is set lower than the viscosity V1 of the positiveelectrode active material layer-forming paste (the viscosity is set tobe low). As a result, a contact angle of the insulating layer formingpaste to the positive electrode current collector 32 is smaller than thecontact angle of the positive electrode active material layer-formingpaste to the positive electrode current collector 32, and the insulatinglayer forming paste can be easily made to be get under the positiveelectrode active material layer-forming paste. Further, a ratio of theviscosity V2 to the viscosity V1 (V2/V1) may be adjusted in the range ofapproximately 0.01 to 0.99, and typically 0.05 to 0.95. Accordingly, thewidth of the overlapping portion B can be adjusted preferably within theabove range.

In Step (S3), the end portion of the positive electrode currentcollector 32 in the Y2 direction is placed, and the two kinds of pastesare applied onto the positive electrode current collector 32. Theapplication of the paste can be performed using a coating device such asa die coater, a slit coater, a comma coater, or a gravure coater. In anexample, the two kinds of pastes are applied in three steps in order.That is, first, coating regions of the first insulating layer 36 a andthe second insulating layer 36 b are coated with the insulating layerforming paste, while leaving the non-coated portion 32A of the positiveelectrode current collector 32. Next, the positive electrode currentcollector 32 and the first insulating layer 36 a are coated with thepositive electrode active material layer-forming paste with apredetermined width La. Then, the insulating layer forming paste isapplied again with a predetermined width Lc to cover the entire endportion of the positive electrode active material layer. Thereafter, thepositive electrode active material layer-forming paste and theinsulating layer forming paste are dried by heating as necessary. As aresult, the positive electrode 30 is coated.

At this time, from the viewpoint of productivity, the positive electrode30 may be coated with a double-width. That is, first, two insulatinglayer forming pastes may be coated such that when the positive electrodeactive material layer is formed to have a width of 2×La, the firstinsulating layer 36 a is positioned at both ends, and the secondinsulating layer 36 b is positioned further separately on both endsides. Then, the positive electrode active material layer-forming pasteis applied between the two first insulating layers 36 a. The drying stepmay be the same as above. As a result, the double-width positiveelectrode 30 is coated.

Alternatively, in another example, as shown in FIG. 5 , in Step (S3),the positive electrode current collector 32 may be simultaneously coatedwith the two kinds of pastes using a die coater. By using the diecoater, the positive electrode provided with the first insulating layer36 a and the second insulating layer 36 b separated from each other canbe preferably applied at one time.

The upper part of FIG. 6 is a schematic view for schematicallyillustrating the configuration of a die coater 100. The middle part ofFIG. 6 is a schematic view showing an approximate dimension anddisposition of the shim plates to be combined with the die coater 100.The lower part of FIG. 6 is a schematic sectional view illustrating theconfiguration of the positive electrode formed by such die coater 100.

A basic configuration of the die coater 100 may be similar to that of aknown die coater used for manufacturing electrodes of the type ofsecondary battery. The die coater 100 includes a set of upper and lowermembers called a die, and a slurry housing portion called a manifold isprovided between a pair of dies. In addition, the die coater isconfigured such that a slit for discharging the slurry housed in themanifold is formed between the dies, and a shape or gap of the slit canbe adjusted at discretion, by inserting or attaching the shim plate inor to the slit or the like. Then, the slurry is supplied to the manifoldin the die by a pump or the like, and the substrate disposed atdischarge port of the slit can be coated with the slurry by dischargingthe slurry in a state of being sheared from the slit.

In some embodiments, the die coater 100 is configured to manufacturedouble-width electrodes. For example, as shown in the upper part of FIG.6 , the die coater 100 includes a first die 102, and a second die 103and a third die 104 provided on both sides of the first die 102. Thedisposition direction of the dies 102, 103, 104 is a direction (forexample, horizontal direction) orthogonal to the delivery direction (forexample, vertical direction) of the substrate. The first die 102 at thecenter is a die for coating the positive electrode active material layer34. The two dies 103, 104 on both sides are dies for coating theinsulating layer 36, respectively. The manifold of the die 102 containsthe positive electrode slurry for forming the positive electrode activematerial layer 34, and the manifold of each of the dies 103, 104contains the insulating layer slurry for forming the insulating layer36.

In the dies 102, 103, 104, a slit is disposed in a straight line alongthe horizontal direction (lateral direction in the drawing). Thepositive electrode slurry and the insulating layer slurry arecontinuously discharged in the width direction like a waterfall from theslit of each of the dies 103, 102, 104, and are supplied sequentiallyonto the positive electrode current collector 32 (substrate) to betransported at a discharge port position of the slit. Accordingly,basically, the insulating layer 36 corresponding to the width of theslit of the die 103, the positive electrode active material layer 34corresponding to the width of the slit of the die 102, and theinsulating layer 36 corresponding to the width of the slit of the die104 are applied to the surface of the positive electrode currentcollector 32 to be adjacent to each other in this order in a strip shapealong the flow direction. Here, the shim plates 111, 112, 113, 114having a shape shown in the middle of FIG. 6 can be attached to the diecoater 100. The shim plates 111, 114 are baffle plates that regulate theinsulating layer paste not to be supplied to a region of the positiveelectrode current collector 32 that should form the non-coated portion32A. The shim plates 112, 113 are baffle plates which partition theinsulating layer 36 to the first insulating layer 36 a and the secondinsulating layer 36 b and sufficiently separate the first insulatinglayer 36 a and the second insulating layer 36 b from each other, suchthat the insulating layer paste is not supplied to the region of thepositive electrode current collector 32 that should form the non-coatedportion 32A. Dimensions such as widths and thicknesses of the shimplates 112, 113 and installation positions can be appropriately adjustedsuch that the first insulating layer 36 a and the second insulatinglayer 36 b having desired dimensions are formed. The drying step may bethe same as above. As a result, the double-width long positive electrode30 is coated.

In Step (S4), the produced positive electrode 30 is slit (cut) asnecessary. The positive electrode 30 formed with a double-width is cutinto two at the center of the positive electrode active material layer34 in the width direction. Accordingly, the positive electrode 30 havinga predetermined width can be obtained. Further, the positive electrodeformed to be long is cut into appropriate lengths in the lengthdirection. Accordingly, the positive electrode 30 having a predeterminedlength can be obtained.

Hereinafter, as a specific example, the non-aqueous electrolytesecondary battery disclosed herein was produced. The present disclosureis not intended to be limited to the following specific examples.

Reference Example

Production of Positive Electrode

A lithium nickel cobalt manganese-containing composite oxide(LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂:NCM) having a layered structure as thepositive electrode active material, acetylene black (AB) as a conductionaid, and polyvinylidene fluoride (PVdF) as a binder were mixed in a massratio of NCM:AB:PVdF=90:8:2 and kneaded with N-methyl-2-pyrrolidone(NMP) as a solvent, and accordingly, a positive electrode paste wasprepared.

Also, boehmite as an inorganic filler (F) and PVdF as a binder (B) weremixed in a mass ratio of F:B=90:10, and kneaded in NMP as a solvent, andaccordingly, an insulating layer forming paste was prepared.

Then, the prepared positive electrode paste and insulating layer formingpaste were respectively accommodated in a positive electrode pasteaccommodating portion and an insulating layer paste accommodatingportion of the die coater (the die coater described above) shown in FIG.4 . The shim plates 111, 114 for forming the non-coated portion of thepositive electrode current collector were installed in the die coater,and other shim plates 112, 113 were not installed. Then, two kinds ofpastes were applied at the same time to a long aluminum foil having athickness of approximately 12 μm as a positive electrode currentcollector, dried, and then slit (cut) at the center in the widthdirection, and further cut to have a predetermined length, andaccordingly the positive electrode was produced. In this case, theviscosities of both pastes were adjusted such that the ratio (V2/V1) ofthe viscosity V2 of the insulating layer forming paste to the viscosityV1 of the positive electrode paste was approximately 0.4.

The obtained positive electrode is provided with the positive electrodeactive material layer, the insulating layer, and the non-coated portionon the surface of the positive electrode current collector in this orderin the width direction. Also, in the positive electrode, it wasconfirmed that the insulating layer was formed to be adjacent to the endportion of the positive electrode active material layer in the widthdirection, and such that in the adjacent position, a part thereof wasinterposed between the positive electrode current collector and the endportion of the positive electrode active material layer and covers theend portion of the positive electrode active material layer. Thethickness (flat portion) of the positive electrode active material layerwas fixed at approximately 52 μm. The dimension of the insulating layerin the width direction was fixed with a length of 120%, when thedistance from the end portion E of the positive electrode activematerial layer to a point X where the end portion of the negativeelectrode active material layer is positioned when facing the negativeelectrode to be described later is 100%. The positive electrodes ofReference Examples 1 to 7 were obtained by changing the thickness (flatportion) of the insulating layer between 1 μm and 100 μm as shown inTable 1 below. The thickness of the insulating layer was adjusted bychanging a gap with a shim plate installed between the two dies of thedie coater. In the positive electrode of Reference Example 7, thethickness of the insulating layer is significantly thicker than thethickness of the positive electrode active material layer.

Production of Negative Electrode

Graphite (C) as a negative electrode active material, styrene butadienerubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as athickener were mixed in a mass ratio of C:SBR:CMC=98:1:1, and a negativeelectrode paste was prepared by blending and kneading with ion-exchangedwater. Then, the prepared negative electrode paste was applied to a longcopper foil having a thickness of 8 μm as a negative electrode currentcollector using a die coater, dried and then slit (cut) at the center inthe width direction. Further, a negative electrode having a negativeelectrode active material layer was obtained by cutting in apredetermined length. In order to collect current, the negativeelectrode was provided with non-coated portions, in which the negativeelectrode active material layer was not formed, on both end portions inthe width direction before slitting.

Production of Evaluation Cell

The positive electrode and the negative electrode of each exampleprepared above were stacked to be insulated from each other via aseparator to form a layered product. The layered product was housed in alaminate bag together with a non-aqueous electrolytic solution. As theseparator, a porous sheet having a three-layer structure of PP/PE/PP wasused. As the non-aqueous electrolytic solution, a mixed solventcontaining ethylene carbonate (EC), ethylmethyl carbonate (EMC), anddimethyl carbonate (DMC) in a volume ratio of EC:EMC:DMC=3:3:4 in whichLiPF₆ as a supporting salt was dissolved at a concentration of 1 mol/Lwas used. Accordingly, laminate cells of Reference Examples 1 to 7 wereconstructed. 10 laminate cells were prepared for each example in orderto reduce the influence of manufacturing variations.

Overcharge Test

The laminate cells of each example were charged at a constant current(CC) at a rate of about 1/3 C until the voltage reached 4.1 V under atemperature environment of and then charged at a constant voltage (CV)until the current reached about 1/50 C. Accordingly, the cells of eachexample were subjected to an activation treatment. Next, a state ofcharge (SOC) of the cells were defined as SOC 100%, and CC discharge wasperformed at a rate of about 1/3 C until the voltage reached 3V. Thedischarge capacity at this time was recorded and the state of charge ofthe cell with the voltage of 3V was defined as SOC 0%.

Then, a thermocouple was attached to the center of the laminate cell onthe outside (bag surface) of each example, and CC charging was performedat a rate of 100 C under a temperature environment of 25° C. until thecell voltage reached 5.1 V (overcharged state). At this time, thehighest temperature of the cell was recorded and a temperature risewidth (° C.) from 25° C. was calculated. Then, the temperature risewidth (arithmetic mean value) of the cells of each example wasstandardized with the temperature rise width (arithmetic mean value) ofthe laminate cell of Reference Example 7 as a reference (100%), andresults thereof were shown in Table 1.

TABLE 1 Thickness of Temperature Reference insulating rise rate Examplelayer [μm] (%) 1 1 130 2 3 118 3 5 109 4 8 100 5 10 99 6 20 101 7 100100

As shown in Table 1, in the cells of Reference Examples 4 to 7 in whichthe thickness of the insulating layer was 8 μm or larger, there wasalmost no heat generation due to overcharge, and therefore a temperaturerise rates of the cells were almost the same as each other as 99% to101%. On the other hand, in the cells of Reference Examples 1 to 3 inwhich the thickness of the insulating layer was smaller than 8 μm, thetemperature rise rate due to overcharge significantly exceeds 100%, andwas 109% to 130%. It was found that the smaller the thickness of theinsulating layer, the larger the temperature rise rate.

In the laminate cell of Reference Example 7, since the thickness of theinsulating layer was sufficiently thicker than the thickness of thepositive electrode active material layer, it is unlikely that a shortcircuit will occur in the region where the insulating layer was formed.From above, it is considered that a minute short circuit in theovercharged state is preferably suppressed, not only in the cells ofReference Example 7 but also in the cells of Reference Examples 4 to 6.

On the other hand, in the cells of Reference Examples 1 to 3, thesmaller the thickness of the insulating layer, the higher thetemperature rise rate. Therefore, it is considered that a minute shortcircuit occurs at any position where the insulating layer was provided,which causes extra heat generation, and cell temperatures increased dueto the occurrence. Here, the cut end portion of the negative electrodewas positioned at the end portion of the negative electrode facing theinsulating layer, but it was confirmed that burrs are easily generatedin the negative electrode current collector at the time of cutting thenegative electrode. Malleability of metal is higher in the order ofAu>Ag>Cu>Al. However, Cu tends to generate burrs in the work of cuttingthe current collector, but Al does not generate many burrs. It wasconfirmed that even if the burrs of the negative electrode currentcollector were large, it did not grow to the same height as thethickness of the negative electrode current collector. From the above,in the cells of Reference Examples 1 to 3, it was considered that burrsdue to the cutting of the negative electrode current collector at theend portion of the negative electrode were generated, and the presenceof these burrs caused a physical minute short circuit, or a potentialwas concentrated at the burr position and locally reached a high voltageso that the decomposition of the active material was promoted.

From the above, it can be said that it is effective to provide theinsulating layer at least at a position facing the cut end portion ofthe negative electrode (that is, the cut position of the end portion ofthe negative electrode active material layer). In addition, it can besaid that the thickness of the insulating layer is preferably equal toor larger than the thickness of the negative electrode current collectorin consideration of the generation of burrs on the negative electrodecurrent collector.

Test Example

Production of Positive Electrode

Positive electrodes of Examples 1 to 6 were produced in the same manneras in Reference Example 4 (thickness of insulating layer: 8 μm) exceptfor the followings. Then, the laminate cells of Examples 1 to 6 wereproduced, using the positive electrodes of Examples 1 to 6, in the samemanner as in the reference example. In addition, 10 laminate cells wereprepared for each example, for each of the following evaluation tests,in order to reduce the influence of manufacturing variations.

Example 1

In the positive electrodes of Example 1, the positive electrodes havingno insulating layer were produced using the positive electrode pastealone without using the insulating layer forming paste.

Example 2

In Example 2, first, the positive electrode active material layerwithout forming the insulating layer was formed of the positiveelectrode paste alone (the same as the positive electrode of Example 1).Next, the insulating layer forming paste was accommodated in both thepositive electrode paste accommodating portion and the insulating layerpaste accommodating portion of the die coater, and the currentcollecting part was left as a non-coated portion, and an insulatinglayer having a thickness of 8 μm was formed on the entire surface of theother positive electrode, using the shim plates 111, 114 alone. As aresult, the positive electrode having a structure in which a regionserving as a current collecting part (welding part) of the positiveelectrode current collector of Example 1 was a non-coated portion alongthe end portion in the width direction, and the insulating layer wasprovided on the entire surface of the other region.

Example 3

In Example 3, the shim plates 112, 113 for dividing the insulating layerforming paste into two strips and the shim plates 111, 114 for formingthe non-coated portion of the positive electrode current collector wereinstalled in a slit part of the die coater that discharges theinsulating layer forming paste, and the positive electrode activematerial layer, the first insulating layer, the non-coated portion, thesecond insulating layer, and the non-coated portion were formed on thepositive electrode current collector in this order in the widthdirection. Each of the shim plates 111, 112, 113, 114 was adjusted inposition and dimension such that the first insulating layer was formedto be adjacent to the positive electrode active material layer, and suchthat in the adjacent position, a part thereof was interposed between thepositive electrode current collector and the end portion of the positiveelectrode active material layer and covers the end portion of thepositive electrode active material layer. Also, the position wasadjusted such that the second insulating layer was formed at a positionfacing the end portion of the negative electrode active material layer.Further, the shim plate was adjusted in position and dimension, suchthat the dimension of the first insulating layer in the width directionwas 20% from the end portion E toward the point X, when the distancefrom the end portion E of the positive electrode active material layerto the point X where the end portion of the facing negative electrodeactive material layer was positioned was 100%. Also, the shim plate wasadjusted in position, dimension, and gap, such that the dimension of thesecond insulating layer in the width direction was 10% from the point Xtoward the end portion E and 10% toward the opposite side (end portionside of the current collector) (total 20%) and the thickness (flatportion) was 8 μm.

Example 4

In Example 4, the positive electrode active material layer and the firstinsulating layer were formed in the same manner as in Example 3, andeach of the shim plates was adjusted in position and dimension such thatthe dimension of the second insulating layer in the width direction is20% from the point X toward the end portion E, and 20% toward theopposite side (total 40%).

Example 5

In Example 5, the positive electrode active material layer and the firstinsulating layer were formed in the same manner as in Example 3, andeach of the shim plates was adjusted in position and dimension such thatthe dimension of the second insulating layer in the width direction is50% from the point X toward the end portion E, and 50% toward theopposite side (total 100%).

Example 6

In Example 6, the positive electrode active material layer and the firstinsulating layer were formed in the same manner as in Example 3, andeach of the shim plates was adjusted in position and dimension such thatthe dimension of the second insulating layer in the width direction is50% from the point X toward the end portion E, and 20% toward theopposite side (total 70%).

Overcharge Test

When the overcharge test was performed on the laminate cells in eachexample, in the same manner as in the reference example, the highesttemperature of the cell was recorded and a temperature rise width (° C.)from 25° C. was calculated. Then, the temperature rise width (arithmeticmean value) of the cells of each example was standardized with thetemperature rise width (arithmetic mean value) of the laminate cell ofExample 2 in which the insulating layer was provided on the entiresurface except for a current collecting part as a reference (100%), andresults thereof were shown in Table 2 below.

Low Temperature Resistance Measurement

First, the laminate cells of each example were charged at a constantcurrent (CC) at a rate of about 1/3 C until the voltage reached 4.2 Vunder a temperature environment of 25° C., and then charged at aconstant voltage (CV) until the current value reached 1/50 C. The stateof charge (SOC) was defined as full charge (SOC 100%). After that, arest period was provided for 5 minutes, and CC discharge was performedat a rate of 1/3 C up to 3.0 V, thereby performing an initial chargetreatment. A IV resistance value (arithmetic mean value) when the cellsof each example after the initial charging were charged to SOC 60% at aconstant current of 15 C in an environment of −10° C. was calculated,and results thereof were shown in Table 2 below. In addition, Table 2shows the values when the IV resistance value (arithmetic mean value) ofthe batteries of Example 1 having no insulating layer was standardized(100%).

TABLE 2 Dimension from point X Current Temperature End Portion collectorend rise Resistance Reference E side portion side rate value Example [%][%] (%) [%] 1 None None 150 100 2 Entire surface on None 100 110positive electrode active material layer 3 10 10 120 102 4 20 20  99  985 50 50 101 109 6 50 20 100 101

As shown in Table 2, it was confirmed that the laminate cell of Example1 in which the insulating layer was not provided on the positiveelectrode had the second lowest resistance value among all the examples,and it was found that formation of the insulating layer on the electrodecan cause an increase in the internal resistance of the cell. However,in the laminate cells of Example 1, it was found that a minute shortcircuit occurs at the time of overcharging, and the temperature riserate reaches 150%, which is an extremely high temperature. From theabove, it can be said that it is preferable to provide the insulatinglayer in consideration of the safety of the battery.

Next, in the laminate cells of Example 2 in which the entire surface ofthe positive electrode other than the current collecting part wascovered with an insulating layer having an appropriate thickness, it wasconfirmed that the temperature rise rate was the second lowest in allcases, and a minute short circuit occurred in the overcharged state wassufficiently suppressed. However, as shown in Table 2, the laminatecells of Example 2 have the highest resistance. It was confirmed that inthe cells of Example 2, the insulating layer was excessively providedwhen compared with the other examples, and this insulating layer becamean internal resistance. From the above, it can be said that it ispreferable to provide the insulating layer just at an appropriateposition in consideration of reduction of the resistance of the battery.

In the laminate cell of Example 3, the insulating layer was providedseparately for the first insulating layer and the second insulatinglayer, and for example, it was confirmed that the resistance wassignificantly reduced as compared with the cells of Example 2. From theabove, it can be said that the insulating layer is preferably providedon an appropriate position with the first insulating layer and thesecond insulating layer separated from each other. However, it was foundthat the laminate cell of Example 3 recorded a high rate of temperaturerise during overcharge, following Example 1. Thus, it is suggested thata minute short circuit occurred during overcharge. In the laminate cellsof Example 3, the second insulating layer was formed just in a narrowrange (width) of 10% inward and outward in the width direction centeringon the point X. Therefore, depending on the coating accuracy of theinsulating layer or the active material layer, the dimensional accuracyof the electrodes, the variation in the overlapping accuracy of thepositive electrode and the negative electrode, the second insulatinglayer may not be disposed at a position sufficiently corresponding tothe burr generation position, generated at an end portion of thenegative electrode current collector, and it is expected that it isdifficult to suppress the internal short circuit stably. Therefore, whenthe insulating layer is provided separately for the first insulatinglayer and the second insulating layer, it can be said that it ispreferable to design the dimension of the second insulating layer to bea little wider.

In the laminate cells of Example 4, the insulating layer is divided intothe first insulating layer and the second insulating layer, and thesecond insulating layer is formed in a range (width) of 20% inward andoutward in the width direction centering on the point X. In this case,it was found that both the temperature rise rate and the resistancevalue were the lowest values of all the examples and were preferable.From the above, it was found that the influence seen in Example 3 suchas coating accuracy of the insulating layer or the active materiallayer, the dimensional accuracy of the electrodes, the variation in theoverlapping accuracy of the positive electrode and the negativeelectrode can be followed by forming the second insulating layer withthe dimensions of 20% each inside and outside centering on the point X.In order to successfully alleviate such manufacturing variations, it canbe said that the second insulating layer preferably has a total width ofabout 40% centering on the point X. Also, it can be said that the sameapplies to the dimensions of the first insulating layer.

In the laminate cells of Example 5, the insulating layer is providedseparately for the first insulating layer and the second insulatinglayer, but the gap is relatively small, and the dimension from the pointX of the second insulating layer to the outer side in the widthdirection is relatively wide at 50%. Therefore, it was confirmed thattemperature rise rate was almost the same low value as the cells ofExample 2 in which the insulating layer was provided on the entiresurface, but the resistance value was also a high value comparable tothat of Example 2. On the other hand, in the laminate cells of Example6, the dimension from the point X of the second insulating layer towardthe inner side in the width direction is the same as that of Example 5,and the dimension toward the outer side is narrowed to 20%. As a result,the cells of Example 6 have a slightly higher temperature rise rate anda higher resistance than those of the cells of Example 4, but theresistance is significantly reduced as compared with the cells ofExample 5. From above, it is suggested that by securing the widenon-coated portion having no insulating layer near the end portion ofthe electrode in the width direction, disposition of an insulatinglayer, which becomes a resistance component, near the current collectingpart is avoided, and current collection efficiency is improved. Fromabove, it can be said that it is preferable that the second insulatinglayer is not provided excessively wide toward the outer side in thewidth direction.

From the above, it can be said that the insulating layer is preferablyprovided on an appropriate position with the first insulating layer andthe second insulating layer separated from each other. It can be saidthat the second insulating layer may be formed about more than 10% (forexample, 20% or more) and 50% or less (for example, 40% or less) inwardin the width direction with the point X corresponding to the end portionof the facing negative electrode as a center. The first insulating layermay be formed by being separated from the second insulating layer and,for example, 70% or less, preferably 50% or less, for example 30% orless, from the end portion E of the positive electrode active materiallayer toward the outer side in the width direction (point X side). Itcan be said that the first insulating layer is preferably formed to be20% or more from the viewpoint of manufacturing variations.

Specific examples of the present disclosure have been described above indetail, but these are merely examples and do not limit the scope of theclaims. The technology described in claims includes variousmodifications and changes of the specific examples illustrated above.

What is claimed is:
 1. A non-aqueous electrolyte secondary batterycomprising: a positive electrode; a negative electrode facing thepositive electrode; and a non-aqueous electrolyte, wherein: the positiveelectrode includes a positive electrode current collector, a positiveelectrode active material layer which is provided on a part of a surfaceof the positive electrode current collector and contains a positiveelectrode active material, and an insulating layer which is provided onother parts of the surface of the positive electrode current collector;the negative electrode includes a negative electrode current collector,and a negative electrode active material layer which is provided on apart of a surface of the negative electrode current collector andcontains a negative electrode active material; and the insulating layerincludes a first insulating layer disposed along an end portion of thepositive electrode active material layer, and a second insulating layerformed at a position which is separated from the first insulating layerand faces an end portion of the negative electrode active materiallayer; wherein the first insulating layer and the second insulatinglayer are separated from each other in a width direction of the positiveelectrode; wherein the positive electrode active material layer has, ina sectional view, a flat region where the surface of the positiveelectrode active material layer is flat and has a substantially uniformthickness, and an end portion region where the surface of the positiveelectrode active material layer is curved toward the positive electrodecurrent collector at an end portion of the positive electrode activematerial layer; and wherein a part of the end portion region is stackedon the first insulating layer.
 2. The non-aqueous electrolyte secondarybattery according to claim 1, wherein an average thickness of the secondinsulating layer is equal to or greater than a thickness of the negativeelectrode current collector.
 3. The non-aqueous electrolyte secondarybattery according to claim 1, wherein the first insulating layer isformed to be interposed between the positive electrode current collectorand the end portion of the positive electrode active material layer andto cover the end portion of the positive electrode active materiallayer.
 4. The non-aqueous electrolyte secondary battery according toclaim 1, wherein an end portion of the negative electrode on a sidefacing the second insulating layer is formed by a cut surface.
 5. Thenon-aqueous electrolyte secondary battery according to claim 1, whereinthe positive electrode current collector comprises a non-coated portionbetween the first insulating layer and the second insulating layer. 6.The non-aqueous electrolyte secondary battery according to claim 1,wherein the positive electrode layer active material has an end portionthe comprises a first inclined surface partly covered by the firstinsulating layer, and a second inclined surface closer to the positiveelectrode current collector than the first inclined surface, the secondinclined surface being entirely covered with the first insulating layer.7. The non-aqueous electrolyte secondary battery according to claim 1,wherein the surface of the positive electrode active material layer iscurved such that the thickness of the positive electrode active materiallayer decreases toward the end portion of the positive electrode activematerial layer.
 8. The non-aqueous electrolyte secondary batteryaccording to claim 1, wherein the positive electrode active materiallayer has, in a sectional view, a flat region where the surface of thepositive electrode active material layer is flat and has a substantiallyuniform thickness, and an end portion region where the surface of thepositive electrode active material layer is curved such that thethickness of the positive electrode active material layer decreasestoward the end portion of the positive electrode active material layer.9. The non-aqueous electrolyte secondary battery according to claim 1,wherein the insulating layer comprises an inorganic filler.
 10. Anon-aqueous electrolyte secondary battery comprising: a positiveelectrode; a negative electrode facing the positive electrode; and anon-aqueous electrolyte, wherein: the positive electrode includes apositive electrode current collector, a positive electrode activematerial layer which is provided on a part of a surface of the positiveelectrode current collector and contains a positive electrode activematerial, and an insulating layer which is provided on other parts ofthe surface of the positive electrode current collector; and theinsulating layer includes a first insulating layer disposed along an endportion of the positive electrode active material layer, and a secondinsulating layer formed at a position which is separated from the firstinsulating layer and faces an end portion of the negative electrodeactive material layer; wherein the first insulating layer and the secondinsulating layer are separated from each other in a width direction ofthe positive electrode; wherein the positive electrode active materiallayer has, in a sectional view, a flat region where the surface of thepositive electrode active material layer is flat and has a substantiallyuniform thickness, and an end portion region where the surface of thepositive electrode active material layer is curved toward the positiveelectrode current collector at an end portion of the positive electrodeactive material layer; and wherein a part of the end portion region isstacked on the first insulating layer.
 11. The non-aqueous electrolytesecondary battery according to claim 10, wherein an average thickness ofthe second insulating layer is equal to or greater than a thickness of acurrent collector of the negative electrode.
 12. The non-aqueouselectrolyte secondary battery according to claim 10, wherein the firstinsulating layer is formed to be interposed between the positiveelectrode current collector and the end portion of the positiveelectrode active material layer and to cover the end portion of thepositive electrode active material layer.
 13. The non-aqueouselectrolyte secondary battery according to claim 10, wherein an endportion of the negative electrode on a side facing the second insulatinglayer is formed by a cut surface.
 14. The non-aqueous electrolytesecondary battery according to claim 10, wherein the positive electrodecurrent collector comprises a non-coated portion between the firstinsulating layer and the second insulating layer.
 15. The non-aqueouselectrolyte secondary battery according to claim 10, wherein thepositive electrode layer active material has an end portion thecomprises a first inclined surface partly covered by the firstinsulating layer, and a second inclined surface closer to the positiveelectrode current collector than the first inclined surface, the secondinclined surface being entirely covered with the first insulating layer.16. The non-aqueous electrolyte secondary battery according to claim 10,wherein the surface of the positive electrode active material layer iscurved such that the thickness of the positive electrode active materiallayer decreases toward the end portion of the positive electrode activematerial layer.
 17. The non-aqueous electrolyte secondary batteryaccording to claim 10, wherein the positive electrode active materiallayer has, in a sectional view, a flat region where the surface of thepositive electrode active material layer is flat and has a substantiallyuniform thickness, and an end portion region where the surface of thepositive electrode active material layer is curved such that thethickness of the positive electrode active material layer decreasestoward the end portion of the positive electrode active material layer.18. A method of forming a non-aqueous electrolyte secondary batterycomprising the steps of: forming a positive electrode; forming anegative electrode facing the positive electrode; and forming anon-aqueous electrolyte, wherein: the positive electrode includes apositive electrode current collector, a positive electrode activematerial layer which is provided on a part of a surface of the positiveelectrode current collector and contains a positive electrode activematerial, and an insulating layer which is provided on other parts ofthe surface of the positive electrode current collector; the negativeelectrode includes a negative electrode current collector, and anegative electrode active material layer which is provided on a part ofa surface of the negative electrode current collector and contains anegative electrode active material; and the insulating layer includes afirst insulating layer disposed along an end portion of the positiveelectrode active material layer, and a second insulating layer formed ata position which is separated from the first insulating layer and facesan end portion of the negative electrode active material layer; whereinthe first insulating layer and the second insulating layer are formedseparated from each other in a width direction of the positiveelectrode; wherein forming the positive electrode comprises forming thepositive electrode active material layer to have, in a sectional view, aflat region where the surface of the positive electrode active materiallayer is flat and has a substantially uniform thickness, and an endportion region where the surface of the positive electrode activematerial layer is curved toward the positive electrode current collectorat an end portion of the positive electrode active material layer; andforming a part of the end portion region such that it is stacked on thefirst insulating layer.
 19. The method of forming a non-aqueouselectrolyte secondary battery of claim 18, further comprising formingthe second insulating layer with an average thickness equal to orgreater than a thickness of the negative electrode current collector.20. The method of forming a non-aqueous electrolyte secondary battery ofclaim 18, further comprising forming the first insulating layer to beinterposed between the positive electrode current collector and the endportion of the positive electrode active material layer and to cover theend portion of the positive electrode active material layer.